The NL East leader obtained Cabrera and cash from the Cleveland Indians for shortstop Zach Walters at Thursday's non-waiver trade deadline.
"He's battle-tested," Nationals general manager Mike Rizzo said of Cabrera. "He's been in the playoffs before. He's been through pennant races. He's a terrific two-way player. He's a great defensive middle infielder."
The 28-year-old Cabrera has spent most of his career at shortstop but has played 162 games at second base, most recently in 2009.
Nationals manager Matt Williams called Cabrera an "everyday player" who'll see the majority of his time at second.
Regular second baseman Anthony Rendon has shifted over to third in place of Zimmerman, who has been out since July 23 with a strained right hamstring. There's no timetable yet for his return.
Washington (58-47) began the day 1 1-2 games ahead of Atlanta in the NL East, but is 3-4 -- including a pair of shutout losses -- since Zimmerman was went down.
In those games, Nationals second baseman, including Walters, Danny Espinosa and Kevin Frandsen, are 6 for 26 (.231).
"You know, like we've always said, we like the team that we have," Rizzo said. "And when Zim went down, to protect ourselves we felt that we should go out and get ourselves a good veteran person to fit into the lineup."
The switch-hitting Cabrera is in the last year of a three-year contract and with top prospect Francisco Lindor at Triple-A Columbus, Cleveland had the flexibility to make the move.
"That's the business," Cabrera said, his voice quavering several times as he spoke with reporters in Cleveland. "It surprised me a little bit, but there is nothing I could do. I knew this was going to be possible. Today when I got here, I didn't even know it was happening."
Oft injured, Cabrera is a career .270 hitter, with 82 home runs and a .331 on-base percentage in eight seasons. He is batting .246 with 33 extra-base hits this season.
"This was the team that gave me the opportunity to play. It's hard, it's hard. It was like I grew up here," he said, indicating he'll join the Nationals on Friday.
Cabrera's 7-year-old son, Meyer Cabrera, maintained his daily routine after the trade. He fielded groundballs while wearing an Indians uniform on the diamond.
Walters, 24, has hit .234 with three home runs and six RBIs in 40 games for the Nationals over the last two seasons.
The switch-hitting infielder was originally acquired from the Diamondbacks on July 30, 2011, for right-handed pitcher Jason Marquis.